Short for Final Fantasy XI, a Massively Multi-Player Online Role-Playing Game (MMORPG) developed by Square-Enix in 2001. Follows several Final Fantasy 'guidelines' for game design: in-depth storyline that takes much time to traverse and complete, detailed graphics, highly-recognizable music, chocobos, airships, and (of course) Cid.
FFXI is a monthly-payment MMORPG and is constantly updated by the developer. Comparable to many other MMORPGs of this age, FFXI is somewhat inexpensive and is well-kept due to the monthly fee (if there was no playing fee, there would be no development/upkeep). According to the last report given by Square-Enix, there were over 500,000 players active with over 1.5 million characters by the third year of gameplay. Though several players have switched over to play other MMORPGs or have left the online game-play world completely, there is near-constantly more players entering the realm of Vana'Diel.
Known for: ability to change character jobs/classes without having to create a new character; having various tradeskills enabling players to create hundreds of items to sell/use; vast and graphical landscapes, underground areas, and building-type structures; various modes of transportation, including chocobo, airship, ferry, and teleportation; extremely long storyline in which players must undergo NPC-given missions to learn more about; and much more.